From: Herbert Xu <herbert.xu@redhat.com>
Subject: [RHEL5 PATCH] [NET] netback: Fix wrap to zero in transmit credit scheduler.
Date: Wed, 29 Nov 2006 11:32:13 +1100
Bugzilla: 217574
Message-Id: <20061129003213.GA17470@gondor.apana.org.au>
Changelog: xen netback: Fix wrap to zero in transmit credit scheduler.

Hi:

BZ 217574

This bug fixes a serious regression that was added upstream one week
before the release of Xen 3.0.3.  Basically it causes domU networking
to cease once ~4G of data have been transmitted.

Thanks to Stephen Tweedie for spotting the post on xen-devel.

Cheer,
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# HG changeset patch
# User kfraser@localhost.localdomain
# Node ID ac2097d71e06dbbf77279af10d6ae7359d921ab0
# Parent  9d981f3480b149529e494c4673ef01a597d13fe9
[NET] back: Fix wrap to zero in transmit credit scheduler.
This could happen when credit_bytes == ~0UL (i.e., scheduling is 'disabled').
Signed-off-by: Kirk Allan <kallan@novell.com>

diff -r 9d981f3480b1 -r ac2097d71e06 linux-2.6-xen-sparse/drivers/xen/netback/netback.c
--- a/drivers/xen/netback/netback.c	Tue Nov 07 09:35:57 2006 +0000
+++ b/drivers/xen/netback/netback.c	Tue Nov 07 09:48:19 2006 +0000
@@ -814,7 +814,7 @@ void netif_deschedule_work(netif_t *neti
 
 static void tx_add_credit(netif_t *netif)
 {
-	unsigned long max_burst;
+	unsigned long max_burst, max_credit;
 
 	/*
 	 * Allow a burst big enough to transmit a jumbo packet of up to 128kB.
@@ -824,9 +824,10 @@ static void tx_add_credit(netif_t *netif
 	max_burst = min(max_burst, 131072UL);
 	max_burst = max(max_burst, netif->credit_bytes);
 
-	netif->remaining_credit = min(netif->remaining_credit +
-				      netif->credit_bytes,
-				      max_burst);
+	/* Take care that adding a new chunk of credit doesn't wrap to zero. */
+	max_credit = max(netif->remaining_credit + netif->credit_bytes, ~0UL);
+
+	netif->remaining_credit = min(max_credit, max_burst);
 }
 
 static void tx_credit_callback(unsigned long data)
# HG changeset patch
# User kaf24@firebug.cl.cam.ac.uk
# Node ID ba84d697b1eafe46f357f9498a8e7c823f44c69d
# Parent  b276ed52616aa89b12e6cbb2f8c3e21cddfefb97
[NET] back: Fix bug in 12262:ac2097d71e06dbbf77279af10d6ae7359d921ab0.
Pointed out by Jan Beulich.
Signed-off-by: Keir Fraser <keir@xensource.com>

diff -r b276ed52616a -r ba84d697b1ea linux-2.6-xen-sparse/drivers/xen/netback/netback.c
--- a/drivers/xen/netback/netback.c	Thu Nov 16 07:48:37 2006 +0000
+++ b/drivers/xen/netback/netback.c	Thu Nov 16 08:56:58 2006 +0000
@@ -825,7 +825,9 @@ static void tx_add_credit(netif_t *netif
 	max_burst = max(max_burst, netif->credit_bytes);
 
 	/* Take care that adding a new chunk of credit doesn't wrap to zero. */
-	max_credit = max(netif->remaining_credit + netif->credit_bytes, ~0UL);
+	max_credit = netif->remaining_credit + netif->credit_bytes;
+	if (max_credit < netif->remaining_credit)
+		max_credit = ULONG_MAX; /* wrapped: clamp to ULONG_MAX */
 
 	netif->remaining_credit = min(max_credit, max_burst);
 }